Up until now, various photo cationically polymerizable compositions have been designed which cationically polymerize and cure upon irradiation with light. Photo cationically polymerizable compositions of this kind contain a photo cationic polymerization initiator activated by irradiation with light and a cationically polymerizable compound in which cationic polymerization is induced by the activated photo cationic polymerization initiator.
An onium salt and an iron arene complex, for example, are used as the above-mentioned photo cationic polymerization initiator. Further, an epoxy compound, a vinyl ether compound, a compound having an oxetane group, or a compound having an alkoxysilyl group is used as the above-mentioned cationically polymerizable compound.
The photo cationically polymerizable compositions are considered to be used for a paint, a coating agent, a varnish, a matrix of a composite, a stereolithography material, an adhesive, a pressure-sensitive adhesive, or the like. Use of an epoxy compound as the photo cationically polymerizable composition particularly makes it possible to increase the adhesion force, creep resistance, weather resistance, water resistance, heat resistance, chemical resistance, and the like of a cured product produced from the composition.
A photo cationically polymerizable composition to be used for the above-mentioned various products is desired to have a high cure rate, as well as high adhesion force to an adherend, high weather resistance and the like of a cured product. Further, a photo cationically polymerizable composition to be used for an adhesive is desired to have a long enough pot life during which bonding operation can be performed, and also fast-curing characteristics upon the bonding operation. That is, the adhesive needs to retain, for a certain period of time after irradiation with light, the fluidity, wettability, and adhesion of a degree at which the bonding operation can be performed.
The below mentioned Patent Document 1 discloses as an example of the above photo cationically polymerizable composition a photocurable pressure-sensitive adhesive composition that contains a cationically polymerizable compound having a cationically polymerizable group, a photo cationic polymerization initiator, and a polymer. Here, a (meth)acrylic polymer, a polyester or the like is used as the polymer.    Patent Document 1: JP 2000-144094 A